Sequita Thompson and her husband called 911 at their home in South Sacramento, not knowing the police were already in the couple’s backyard, and in this instance, the couple was presumed to be the threat.

Thompson’s grandson, Stephon Clark, was only 22 years old when he was shot and killed by the police outside of Thompson’s home. The young man was holding a cellphone in his hand that police said they thought was a weapon. The officers proceeded to fire 20 bullets at the unarmed man....